Typically, conventional harps have used a series of levers on each individual string or a set of pedals to mechanically alter the pitch of the strings to enable the instrument to be played in a given key signature. Where complex key changes occur in compositions, the ability of the harp to be retuned within a reasonable amount of time limits what is physically possible to play. Consequently, certain key changes can be difficult to accomplish during certain compositions limiting music selection and style.
Conventional harps may further require the engaging or disengaging of a pedal or lever to physically change the tension of the strings. In the case of a conventional concert harp, foot pedals can only change two of seven like-letter named strings at a time rendering it, in many cases, difficult or impossible to make instantaneous changes to certain keys. Although the levered harp can change the pitch of individual strings, it is cumbersome to change keys due to the very fact that each individual string requires a lever to be flipped for each sharp or flat in a given key and octave.
Learning to manipulate the levers or pedals on a harp is difficult due to the complicated nature of mechanisms and the music theory required. These mechanisms may also require fine-tuning and the service of a technician, from time-to-time, to keep the instrument functioning properly. These mechanisms also have contributed to the high cost of harps.
Another limitation in conventional harps may be their difficulty to transport. A harp with a sound box and tuning mechanisms is heavy and bulky making transport difficult.